1. Field of the Invention
This invention relates to a free radical polymerization process in which free radical sources or initiators normally soluble only in high polarity media (e.g. water) can be used in relatively low polarity media (e.g. acrylate resin systems). The invention also relates to polymerisation catalysts for use in such a process. In one aspect the invention concerns a process for polymerisation of an acrylic monomer adhesive composition using a metal salt applied to a surface as free radical initiator. It also relates to a process for achieving CTV (cure through volume) in an acrylic adhesive joint where a gap is left between two surfaces being joined.
2. Description of the Related Art
Free radical sources or initiators which are insoluble in organic media were previously only usable in water based polymerization systems such as in emulsion polymerizations. U.S. Pat. No. 4 326 049 Rasmussen has described a process for polymerizing olefinic monomeric material comprising adding a water-soluble free radical initiator/phase transfer agent complex to an organic liquid comprising free-radical polymerizable ethylenically unsaturated monomeric material and activating the same to produce free radicals. Several different classes of phase transfer agents are described, but the phase transfer agents specified in the claims are
(i) a cation complex of an alkali or alkaline earth metal or ammonium cation and a neutral donor molecule selected from the group consisting of multidentate compounds, an amine selected from the group consisting of N,N'-dimethylpiperazine, 1,4-diazabicyclo octane, N,N,N',N'-tetramethylethylenediamine, piperazine hexamethyl phosphoric triamide amphoteric compounds; or
(ii) a cation having the formula (A.sub.m M)+ where A is an organic radical having from one to eighteen carbon atoms bonded to M by m covalent linkages and M is an element selected from Groups VA and VIA of the Periodic Table of Elements.
The preferred phase transfer agents are macrocyclic multidentate compounds referred to as "crowns", crown ethers, cryptates or cryptands, or "lantern" or "clam" compounds. The preferred "crowns" are the substituted and unsubstituted member of the 15-crown-5 and 18-crown-6 series, the most preferred being 18-crown-6. The free radical initiators used in the Examples of the Rasmussen Patent are limited to potassium and ammonium salts, more particularly potassium peroxydisulphate.
The present invention provides a free radical polymerisation process which comprises bringing together (a) monomeric material in a relatively low polarity medium, (b) a free radical source or initiator normally soluble only in high polarity media, and (c) a calixarene derivative of the formula ##STR2##
wherein m+n=4, 6 or 8
n=an integer greater than or equal to 1/2(m=n)
R=hydrocarbyl, hydrocarbyloxy, substituted hydrocarbyl, substituted hydrocarbyloxy, aryl, hydrocarbylaryl, aryloxy, hydrocarbylaryloxy, substituted aryl, substituted hydrocarbylaryl, substituted aryloxy, or substituted hydrocarbylaryloxy;
R'=H, hydrocarbyl, aryl, hydrocarbylaryl, substituted hydrocarbyl, substituted aryl, or substituted hydrocarbylaryl;
R"=H, hydrocarbyl or substituted hydrocarbyl.
When m and n are greater than 1, the m aryl groups having the --OR" side chain may be interspersed around the ring between the aryl groups having the --OCH.sub.2 C(O)R side chain.
In the above compounds, the hydrocarbyl groups shall preferably contain from 1 to 10 carbon atoms, more preferably from 1 to 5 carbon atoms and the aryl and hydrocarbylaryl groups shall preferably have from 6 to 20 carbon atoms, more preferably from 6 to 10 carbon atoms. Hydrocarbyl groups are preferred, especially alkyl or alkenyl groups. A substituted derivative of the foregoing may suitably be substituted with one or more halo groups or substituted or interrupted by one or more oxo groups. Halogen may be chlorine, bromine, fluorine or iodine.
In comparative experiments the present Applicants have found the selected calixarene derivatives to be more efficacious than the appropriate "crown" compound in inducing polymerisation and it was also found possible to employ free radical sources or initiators containing transition metals or lanthanides such as ceric ion salts.
In one aspect the present invention provides a free radical polymerisation catalyst comprising a combination of a water-soluble, organic-insoluble initiator and a calixarene derivative of formula I as defined above. In another aspect the invention provides a process for the free radical polymerisation of ethylenically unsaturated monomeric material which comprises bringing together
(a) an organic medium containing the ethylenically unsaturated monomeric material,
(b) a water soluble, organic-insoluble initiator,
(c) a calixarene derivative of formula I as defined above.
In a further aspect, the invention provides a gap-filling adhesive composition comprising an acrylic monomeric material adapted for activation by a metal salt activator, wherein the composition includes a calixarene derivative of formula I.
In yet another aspect the invention provides a gap-filling adhesive composition as defined above wherein the calixarene derivative is used jointly with a halogenated alkyl acrylate or methacrylate which is halogenated on the alkyl portion.
It is believed that the halogenated organic compound assists in solubilising the metal salt in the acrylic monomer composition and facilitates its diffusion through the volume of the adhesive.
The term "acrylic monomer" as used in this Specification includes methacrylic monomers and mixed monomeric materials containing one or more acrylic monomers. The term "initiator" as used in this specification covers not only free radical sources which themselves initiate polymerisation but also compounds which activate the breakdown to free radicals of a free radical source. In the latter case, the free radical source may be soluble in the organic medium with the monomeric material while the activator is normally of low solubility in the organic medium but is solubilised therein because of the presence of the calixarene derivative. However the invention is applicable more widely to free radical sources which are not necessarily polymerisation initiators, and to the transport of free radical sources from a polar phase to a non-polar phase, the polar phase not necessarily being water. For example the low polarity medium may be hexane or petroleum ether while the high polarity phase may be propylene carbonate or dimethylsulfoxide.
Calixarene compounds are known and may be readily synthesised by methods described in C. Gutsche, Acc. Chem. Res., 16, 161-170 (1983) and references cited therein, the appropriate disclosures of which are incorporated herein by reference. Particular methods of synthesis for the calixarene derivatives exemplified herein are described in U.S. Pat. No. 4 556 700 Harris et. al. assigned to Loctite Limited and European Patent Application No. 0 259 016 of Loctite (Ireland) Limited. The most preferred compounds may be represented by formula I wherein R is ethoxy, methoxy, methyl or phenyl, R' is H or t-butyl, R" (if present) is alkyl, alkenyl or substituted alkyl or alkenyl, more particularly methyl, allyl or allyl acetate, and n is 4 or 6. Preparation of calixarene derivatives wherein at least some of the aryl groups have --O--R" substituents is described in European Patent Application No. 0196895 A2 of Loctite (Ireland) Ltd, particularly in Examples 2 and 3 thereof.
The ethylenically unsaturated monomeric material may be any of the monomers described in U.S. Pat. No. 4 326 049 Rasmussen, the disclosure of which is incorporated by reference. Particularly preferred are acrylic monomers which are well known in the art. It may suitably be an acrylate or methacrylate ester of a monohydric, dihydric, trihydric or polyhydric alcohol. It may include as a modifier or auxiliary polymerisable agent an epoxy or urethane system, or a prepolymer of a low molecular weight urethane or polyester capped with acrylate groups. It may also be an oligomer of an acrylate monomer.
Organic solvents which are known in the art for free radical polymerization may be used as the organic medium. Suitable examples are listed in U.S. Pat. No. 4 326 049 Rasmussen. Free-radical initiators known in the art may be used as the free radical source. Examples are listed in U.S. Pat. No. 4 326 049 Rasmussen. In addition in accordance with the present invention free-radical sources especially peroxide or hydroperoxide are used in conjunction with activator such as transition metal salt solutions as for example Loctite's Primer N product or copper or cobalt salt solutions described in U.S. Pat. No. 3672942 Loctite, and U.S. Pat. No. 4054480 National Starch and Chemical Corporation.
Activation of the free radical initiators may be achieved by conventional means e.g. by thermal, photochemical or chemical (redox) means.